patch 8.2.1848: crash when passing a NULL string or list to popup_settext()

Problem:    Crashyyyyy passing a NULL string or list to popup_settext().
Solution:   Check for NULL pointers. (closes #7132)
diff --git a/src/popupwin.c b/src/popupwin.c
index 05db1af..777e7d8 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1595,14 +1595,16 @@
     // Add text to the buffer.
     if (text.v_type == VAR_STRING)
     {
+	char_u *s = text.vval.v_string;
+
 	// just a string
-	ml_append_buf(buf, 0, text.vval.v_string, (colnr_T)0, TRUE);
+	ml_append_buf(buf, 0, s == NULL ? (char_u *)"" : s, (colnr_T)0, TRUE);
     }
     else
     {
 	list_T *l = text.vval.v_list;
 
-	if (l->lv_len > 0)
+	if (l != NULL && l->lv_len > 0)
 	{
 	    if (l->lv_first->li_tv.v_type == VAR_STRING)
 		// list of strings
diff --git a/src/testdir/test_popupwin.vim b/src/testdir/test_popupwin.vim
index 187b4f1..1524e78 100644
--- a/src/testdir/test_popupwin.vim
+++ b/src/testdir/test_popupwin.vim
@@ -2363,6 +2363,16 @@
   call popup_close(id)
 endfunc
 
+func Test_popup_settext_null()
+  let id = popup_create('', #{ tabpage: 0 })
+  call popup_settext(id, test_null_list())
+  call popup_close(id)
+
+  let id = popup_create('', #{ tabpage: 0 })
+  call popup_settext(id, test_null_string())
+  call popup_close(id)
+endfunc
+
 func Test_popup_hidden()
   new
 
diff --git a/src/version.c b/src/version.c
index b95e0e9..b0fe5e8 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1848,
+/**/
     1847,
 /**/
     1846,